Investigation into the improved interfacial bonding of active-screen plasma functionalised carbon fibre to epoxy matrix by interfacial testing and Raman mapping

The interfacial performance of carbon fibres (CFs) within a resin matrix is critical to the mechanical properties of CF-reinforced composites. However, the chemically inert and smooth surface of CFs often limits fibre–matrix bonding. This study investigates active-screen plasma nitriding (ASPN) as a surface treatment to enhance the fibre–matrix interphase in CF-epoxy composites of both commercially sized and de-sized CFs. X-ray photoelectron spectroscopy and contact angle measurements confirmed increased surface nitrogen functionalities and improved wettability following treatment. Single fibre push-out tests showed that the interfacial shear strength (IFSS) of sized and de-sized CFs increased by 40% and 52%, respectively. A novel Raman mapping methodology was developed to spatially resolve structural changes on CF surfaces, identifying plasma de-sizing, functionalisation, and etching as distinct surface modification mechanisms. Raman mapping of the fibre–matrix interface further revealed an expanded interphase following ASPN treatment, consistent with enhancements in interfacial properties confirmed through transverse fibre bundle tensile testing. These findings highlight ASPN as an effective method for improving interfacial bonding in CF-reinforced composites. The techniques and insights presented here support the development of high-performance fibre-reinforced composites, where fibre–matrix adhesion is critical to performance.